Method and apparatus for external fixation of small bones

ABSTRACT

An external fixator for securing a first bone portion in a fixed relationship with respect to a second bone portion. The fixator includes a bone screw clamp for receiving a first bone screw which is connected to the first bone portion and which includes a spherical portion. The fixator further includes a bone screw clamp which is operable to receive a second bone screw which is connected to the second bone portion and which has a spherical portion. The fixator also includes a connection member having a radiographic window to permit radiographic examination of the bone fracture, as well as a cantilever member operable to secure the circle portions of the first and second bone screw clamps to the connection member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an orthopedic surgicalprocedure, and more particularly to a method and apparatus for externalfixation of small bones.

2. Description of the Related Art

In various orthopedic surgical procedures, it is often necessary tosecure two or more portions of bone in a relatively fixed relationshipto each other. This need is often a result of a fracture which hasoccurred to the bone. To ensure that the bone can properly regenerateand fuse the fractures of the bone, it is important that the variousbone portions be fixed at the desired position during bone regeneration.

The various external fixators are known for the fixation of small bonesduring a surgical procedure. For example, one particular type of fixatorsold by Orthofix S.r.l. for small bones has two bone screw clamps with abarbell-shaped connector disposed between the bone screw clamps. Thebarbell-shaped connector is captured by a bushing and an apertured nutwhich is able to screw on to the end of each of the bone screw clamps. Acam is used to force the bushing in a direction so as to cause thebushing to force the rounded end of the barbell-shaped connector againstthe apertured nut to secure the position of the barbell-shaped connectorwith respect to the bone screw clamp. The bone screw clamp includes abody which is able to slide on the arm of the bone screw clamp and has acover with a plurality of circular grooves disposed thereon. Thecircular grooves are used to receive a plurality of bone screws.

While fixators of the type described above are effective in fixatingbones, they nevertheless can be the subject of certain improvements. Forexample, it would be useful to have a mechanism by which the memberconnecting the two bone screw clamps can be more rigidly secured thansimply by a cam operating directly against a bushing. In addition, thebarbell-shaped nature of the interconnection between the bone screwclamps limits the ability of the physician to view the fracture in thatthe barbell connector is not radiolucent. In addition, unless thecylindrical grooves in the bone screw clamps are made to exactly matchthe shape of the bone screws, the bone screw clamps would only providetwo point fixation of the bone screws.

SUMMARY OF THE PRESENT INVENTION

According to one aspect of the present invention, the invention relatesto a fixator operable for securing two portions of bone in a fixedrelationship to each other, with the first bone portion having a firstbone screw attached thereto while the second bone portion has a secondbone screw attached thereto. The fixator includes first means forreceiving the first bone screw which has a spherical portion. Inaddition, the fixator includes a second means for receiving a secondbone screw which also has a spherical portion. The fixator furtherincludes means for securing the first means for receiving a first bonescrew to the second means for receiving the second bone screw. The meansfor securing include a connection member which is operable to form aradiographic window to permit radiographic examination of the fracture,as well as a cantilever member operable to secure the spherical portionof said first means for receiving the first bone screw to the connectionmember.

An advantage of the present invention is to provide a method andapparatus for fixation of small bones that more rigidly secures movementof a bone screw clamp with respect to the body of the fixator.

Another advantage of the present invention is to provide a method andapparatus for fixation of small bones which permits radiographicexamination of the fracture site.

Another advantage of the present invention is to provide a method andapparatus for fixation of small bones in which the bone screw clamp isable to provide three point fixation of bone screws.

A related advantage of the present invention is to provide a method andapparatus for securing small bones in which the bone screw clamp ispositioned with respect to the body of the fixator by means of acantilever member.

Another advantage of the present invention is the provision of a methodand apparatus for the fixation of small bones having a cam whichgenerates a relatively large amount of locking force to secure theangular position of the bone screw clamp.

Additional advantages and features of the present invention will becomeapparent from the following description and appended claims, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the apparatus for fixation of small bonesin operative association with a wrist joint according to the teachingsof the preferred embodiment of the present invention;

FIG. 2 is an elevational view of the apparatus for fixation of smallbones shown in FIG. 1 according to the teachings of the preferredembodiment of the present invention;

FIG. 3 is a side elevational view of the apparatus for fixation of smallbones shown in FIG. 2 according to the teachings of the preferredembodiment of the present invention;

FIG. 4 is an elevational view of the cantilever member of the apparatusfor fixation of small bones shown in FIG. 2 according to the teachingsof the preferred embodiment of the present invention;

FIG. 5 is an elevational view of the locking member used in associationwith the apparatus for fixation of small bones shown in FIG. 2 accordingto the teachings of the preferred embodiment of the present invention;

FIG. 6(a)-(c) are elevational views of the locking cam used inconjunction with the apparatus for fixation of small bones shown in FIG.2 according to the teachings of the preferred embodiment of the presentinvention;

FIG. 7 is an elevational view of the compression/distraction mechanismof the apparatus for fixation of small bones shown in FIG. 2 accordingto the teachings of the preferred embodiment of the present invention;

FIG. 8 is an illustration of the apparatus for fixation of small bonesshown in operative association with a set of forceps used to locate theapparatus according to the teachings of the preferred embodiment of thepresent invention;

FIGS. 9(a)-9(b) are illustrations of a drill guide used to locate holesfor receiving bone pins which are used with the apparatus for fixationof bones according to the teachings of the preferred embodiment of thepresent invention; and

FIG. 10 is an illustration of the apparatus for fixation of small bonesaccording to the second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment of the presentinvention is merely exemplary in nature and is in no way intended tolimit the invention or its application or uses.

Referring to FIG. 1, an apparatus 10 for fixation of small bone portions12 and 14 is shown. In particular, the apparatus 10 is illustrated asbeing used to secure a bone fracture 16 which is located in closeproximity to the wrist joint. The apparatus 10 is used to secure thebone portions 12 and 14 in a fixed relationship so as to permit thefractured portions to fuse properly. While the apparatus 10 is shown inconjunction with a wrist joint, it will be appreciated that theapparatus 10 may be used with other joints as well.

The construction of the apparatus 10 will now be described withreference to FIGS. 2 and 3. The apparatus 10 includes a first clampsupport arm 18 and a second clamp support arm 20. The first and secondclamp support arms 18 and 20 are connected to each other by means of aconnection member 22 as will be more fully discussed below. The firstclamp support arm 18 includes an extension portion 24 and a sphericalportion 26. The extension portion 24 of the first clamp support arm 18is used to allow a first bone screw clamp 28 to slide thereon asdescribed below. The spherical projection 26 extends from the extensionportion 24 and is used to engage the connection member 22. In a similarfashion, the second clamp support arm 20 also includes an extensionportion 30 and a spherical portion 32. As with the first clamp supportarm 18, the extension portion 30 is used to allow a second bone screwclamp 34 to slide thereon, while the spherical projection 32 extendsfrom the extension portion 30 and serves to allow engagement with theconnection member 22.

As discussed above, the first and second bone screw support clamps 28and 34 are operable to slide on the first extension portion 24 and thesecond extension portion 30, respectively, and are operable to support aplurality of bone screws 36 after they have been secured to bone. Tosecure the bone screws 36 to the bone screw clamps 28 and 34, the bonescrew clamps 28 and 34 include a plurality of bone screw rests 38. Thebone screw rests 38 contain a V-shaped groove which is operable toengage the sides of the bone screws 36. The bone screw rests 38 aresecured to the bodies 40 and 42 of the bone screw clamps 28 and 34 bystaking a projection extending from the bottom of the bone screw rests38. However, the staking operation is performed such as to allowapproximately 0.002" difference between the length of the projection andthe depth of the bore receiving the projection in the bodies 40 and 42so as to allow limited movement of the bone screw rests 38. This limitedmovement of the bone screw rests 38 allows the bone screw rests 38 tocenter on the bone screws 36 and therefore not cause the bone screws 36to otherwise stress the bone when the bone screws are not preciselyaligned with the groove of the bone screw rests 38.

The bone screw clamps 28 and 34 further each include cover members 46and 48 which are able to be inserted over the bone screws 36 when thebone screws 36 are located in the bone screw rests 38. The cover members46 and 48 each include an aperture 50 which allows a threaded fastener52 to pass through the cover members 46 and 48 and into a threadedaperture of the bodies 40 and 42 of the bone screw clamps 28 and 34.

To secure the position of the bone screw clamps 28 and 34 on theextension portions 24 and 30 of the first and second clamp support arms18 and 20, the apparatus further includes a plurality of locking screws54. The locking screws 54 are operable to threadably engage the bodies40 and 42 of the bone screw clamps 28 and 34 and extend therethrough toengage the extension portions 24 and 30 of the first and second clampsupport arms 18 and 20, respectively. Accordingly, upon rotation of thelocking screws 54, the locking screws 54 are able to engage theextension portions 24 and 30 of the first and second clamp support arms18 and 20 so as to prevent longitudinal movement of the bone supportclamps 28 and 34.

The connection member 22 and the cantilever member 56 will now bedescribed with reference to FIGS. 4 and 5. The connection member 22 isgenerally U-shaped so as to form a radiographic window 58 through whichthe fracture 16 may be viewed. The connection member 22 includes a firstplurality of apertures 60 as well as a second plurality of apertures 62.The first plurality of apertures 60 are operable to receive a lockingpin 64 which extends through the cantilever members 62 as well as theconnection member 22 so as to form a hinge between the connection member22 and the cantilever members 62. The second plurality of apertures 62are used to receive a locking cam 66 which also extends through theapertures of the cantilever members 56. The locking cam 66 (shown inFIG. 6) includes a non-circular camming portion 68 which engages one ofthe second plurality of apertures 62 at an angle which is less than theangle which would be engaged if the cross-section of the camming portion68 were circular in cross-section. Accordingly, the approach angle ofthe camming portion 68 with respect to one of the second plurality ofapertures 62 is reduced so as to allow less resistance to rotation whenthe locking cam 66 is rotated so as to secure the spherical portion ofthe clamp support arm 18 between the cantilever member 56 and theconnection member 22. Accordingly, the locking cam 66 is able togenerate greater force for securing the cantilever member 56 to theconnection member 22 for a given applied torque.

The connection member 22 also has a plurality of central apertures 70which are able to receive the spherical portions 26 and 32 of the firstand second clamp support arms 18 and 20 while each of the cantilevermembers 56 also includes a central aperture 72 which is able to receivepart of the spherical portions 26 and 32 of the first and second clampsupport arms 18 and 20. Accordingly, when the locking cam 66 is rotatedin such a manner so as to displace the cantilever member 56 in adirection towards the connection member 22, the spherical portions 26and 32 of each of the clamp support arms 18 and 20 are securely engagedbetween the connection member 22 and the cantilever members 56.

To allow the bone screws 36 which are disposed within the first bonescrew clamp 28 to be longitudinally displaced, the first clamp supportmember 28 further includes a compression/distraction assembly 74 asshown in FIG. 7. The compression/distraction assembly 74 includes athreaded pin 76 having a head 78 with a hex-shaped recess. The threadedpin 76 is secured to the first clamp support arm 28 by means of a firstmounting member 80 and a second mounting member 82, each of which isattached by means of a threaded fastener 84. The compression/distractionassembly 74 further includes a movable member 86 which threadablyengages the threaded pin 76 of the compression/distraction assembly 74.The movable member 86 includes a pin 88 which engages a recess in thebody 40 of the first bone screw clamp 28. As will be appreciated bythose skilled in the art, rotation of the threaded pin 76 causes themovable member 86 to be displaced with respect to the first and secondmounting members 80 and 82. Because the pin 88 of the movable member 86engages the bone screw clamp 28, the bone screw clamp 28 is also able tomove upon rotation of the threaded pin 76.

It is often necessary to locate the apparatus while the joint inquestion is being subjected to radiation. For this reason, the apparatus10 may also be used with a plurality of forceps 90 shown in FIG. 8. Inthis regard, the forceps 90 include a handle 92 which has a bone screwengaging portion and a rotatable knob 96. The rotatable knob 96 issecured to a threaded member 98 which extends to the bone screw engagingportion 94. Accordingly, by rotation of the knob 96, the bone screwengagement portion 94 can clamp the bone screws 36 in a secure manner.When the forceps 90 are used, the bone screws 36 are initially clampedby the forceps 90 and then the forceps 90 are used to manipulate theposition of the apparatus 10. Once the apparatus 10 is in the properposition, the cams 66 are rotated so as to secure the spherical portions26 and 32 of the clamp support arms 18 and 20 to the connection member22 and the threaded fasteners 54 are rotated so as to secure theposition of the bone screw clamps 28 and 34 with respect to the clampsupport arms 18 and 20.

To facilitate the positioning of the bone screws 36 when using theapparatus 10, a drill guide 100 similar to that shown in FIG. 9 may beused. The drill guide 100 includes a guide portion 102 having twolongitudinal bores 104 extending therethrough. The drill guide 100 alsoincludes a handle portion 106 which may be used to position the guideportion 102. In operation, the guide portion 102 of the drill guide 100is positioned such that the circular projections 106 of the guideportion 102 are received through a soft tissue sleeve (not shown) whichengages the bone screw rests 38 of the bone screw clamps 28 and 34. Adrill is then used to form a hole in the bone and then the drill and thedrill guide 100 are removed. A bone screw 36 is then inserted into thesoft tissue sleeve and then is secured to the bone. The soft tissuesleeve is then removed and then the bone screw is secured to the bonescrew clamp 28 by rotation of the threaded fastener.

The second preferred embodiment of the present invention is shown inFIG. 10. In this embodiment, similar reference numerals will be used toidentify similar components as previously described with respect to thefirst preferred embodiment of the present invention. As with the firstpreferred embodiment of the present invention, the apparatus 10 of thesecond embodiment of the present invention includes a first clampsupport arm 18 and a second clamp support arm 20. A first bone screwclamp 28 is located on the first clamp support arm 18, while a secondbone screw clamp 34 is located on the second clamp support arm 20. Thefirst and second clamp support arms 18 and 20 are connected by aconnection member 22 which is operable to locate the first clamp supportarm 18 at a position which is below and at right angles to the secondbone support arm 20. This allows the apparatus to be used in other formsof fixation of small bones.

In use, the apparatus 10 is initially oriented in the position where itis desired to be ultimately secured to the bone. A soft tissue sleeve(not shown), followed by the drill guide 100, is inserted into the firstbone screw support clamp 28 and onto the bone screw rest 38 of the bonescrew clamp 28. A drill is then used to form two holes in the bone andthen the drill guide 100 is removed from the first bone screw clamp 28.Two bone screws 36 are then inserted into the soft tissue sleeve and arerotated so as to securely engage the bone. The soft tissue sleeve isthen removed from the bone screw clamp 28 and then the cover member 46is secured to the body 40 of the bone screw clamp 28. This process isthen repeated with respect to the bone screws 36 which are inserted intothe second bone screw clamp 34.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willrecognize from such discussion and from the accompanying drawings andclaims, that various changes, modifications and variations can be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus for securing a first bone portion ina fixed relationship to a second bone portion, the apparatuscomprising:a first bone screw connected to the first bone portion; asecond bone screw connected to the second bone portion; means forreceiving said first bone screw, said means for receiving said firstbone screw having a spherical portion; means for receiving said secondbone screw, said means for receiving said second bone screw having aspherical portion; and means for securing said means for receiving saidfirst bone screw to said means for receiving said second bone screw,said means for securing being operative to at least partially define aradiographic window to permit radiographic examination of the fixedrelationship of the first and second bone portions in a directionsubstantially parallel to said first bone screw, said radiographicwindow extending directly between said spherical portion of said meansfor receiving said first bone screw and said spherical portion for saidmeans for receiving said second bone screw.
 2. The apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion of claim 1, wherein said means for securing said means forreceiving said first bone screw to said means for receiving said secondbone screw includes an intermediate portion having a longitudinal axisspaced apart from a line passing through said spherical portion of saidmeans for receiving said first bone screw and said spherical portion ofsaid means for receiving said second bone screw.
 3. The apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion of claim 2, further comprising a cantilevered member operable tosecure the spherical portion of said means for receiving said first bonescrew to said means for securing said means for receiving said firstbone screw to said means for receiving said second bone screw.
 4. Theapparatus for securing a first bone portion in a fixed relationship to asecond bone portion of claim 3, wherein said means for securing saidmeans for receiving said first bone screw to said means for receivingsaid second bone screw comprises a generally U-shaped connecting member,and further wherein said cantilevered member includes a first endpivotally interconnected with said connecting member for selectiverotation through a camming member.
 5. The apparatus for securing a firstbone portion in a fixed relationship to a second bone portion of claim1, wherein said means for receiving said first bone screw includes meansfor longitudinally displacing said first bone screw relative to saidspherical portion of said means for receiving said first bone screw. 6.The apparatus for securing a first bone portion in a fixed relationshipto a second bone portion of claim 1, wherein said means for receivingsaid first bone screw includes means for establishing three pointcontact with said first bone screw.
 7. The apparatus for securing afirst bone portion in a fixed relationship to a second bone portion ofclaim 1, wherein said means for receiving said first bone screw includesa base portion and a cover portion, said base portion and said coverportion cooperatively defining a channel adapted to receive said firstbone screw, one of said base portion and said cover portion including asubstantially V-shaped groove for directly engaging said first bonescrew in two point contact and the other of said base portion and saidcover portion engaging said first bone screw at a third point ofcontact.
 8. An apparatus for securing a first bone portion in a fixedrelationship to a second bone portion by a first bone screw connected tothe first bone portion and a second bone screw connected to the secondbone portion, the apparatus comprising:a first clamping member forreceiving the first bone screw, said first clamping member including aspherical portion; a second clamping member for receiving the secondbone screw, said second clamping member including a spherical portion;and a connecting member for securing said first clamping member to saidsecond clamping member, said connecting member including an intermediateportion having a longitudinal axis spaced apart from a line passingthrough said spherical portion of said first clamping member and saidspherical portion of said second clamping member in a directionsubstantially normal to the first bone screw.
 9. The apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion of claim 8, further comprising a cantilevered member operable tosecure said spherical portion of first clamping member to saidconnecting member.
 10. The apparatus for securing a first bone portionin a fixed relationship to a second bone portion of claim 9, whereinsaid connecting member further includes a transversely extending portiondisposed generally perpendicular to said intermediate portion having anaperture, and further wherein said cantilevered member includes anaperture, said spherical portion of said first clamping member beingcentered between said cantilevered member and said transverselyextending portion such that said spherical portion of said firstclamping member partially extends into said aperture of saidtransversely extending portion and partially extends into said apertureof said cantilevered member.
 11. The apparatus for securing a first boneportion in a fixed relationship to a second bone portion of claim 10,further comprising a camming member for selectively preventing relativerotation between said spherical portion of said first clamping memberand said cantilevered member.
 12. The apparatus for securing a firstbone portion in a fixed relationship to a second bone portion of claim8, wherein said first clamping member includes a longitudinallydisplaceable portion for receiving the first bone screw.
 13. Theapparatus for securing a first bone portion in a fixed relationship to asecond bone portion of claim 12, further comprising a mechanism forincrementally advancing said longitudinally displaceable portionrelative to the spherical portion of said first clamping member.
 14. Theapparatus for securing a first bone portion in a fixed relationship to asecond bone portion of claim 8, wherein said first clamping memberincludes a base portion and a cover portion, and further wherein one ofsaid base portion and said cover portion includes a substantiallyV-shaped groove for directly engaging the first bone screw in two pointcontact and the other of said base portion and said cover engages saidfirst bone screw at a third point of contact.
 15. The apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion of claim 8, wherein said connecting member is generally U-shapedhaving a pair of transversely extending portions disposed generallyperpendicular to said intermediate portion.
 16. An apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion by a first bone screw connected to the first bone portion and asecond bone screw connected to the second bone portion, the apparatuscomprising:a first clamping member for receiving the first bone screw; asecond clamping member for receiving the second bone screw; and aconnecting member for securing said first clamping member to said secondclamping member, said connecting member having a substantially U-shapedconfiguration for at least partially defining a radiographic window topermit radiographic examination of the fixed relationship of the firstand second bone portions.
 17. The apparatus for securing a first boneportion in a fixed relationship to a second bone portion of claim 16,further comprising a cantilevered member operable to secure said firstclamping member to said connecting member.
 18. The apparatus forsecuring a first bone portion in a fixed relationship to a second boneportion of claim 17, wherein said connecting member is unitarily formedand includes an intermediate portion and a transversely extendingportion disposed generally perpendicular to said intermediate portion.19. The apparatus for securing a first bone portion in a fixedrelationship to a second bone portion of claim 18, wherein said firstclamping member includes a spherical portion, and further whereintransversely extending portion includes an aperture and saidcantilevered member includes an aperture, said spherical portion of saidfirst clamping member being centered between said cantilevered memberand said transversely extending portion such that said spherical portionof said first clamping member partially extends into said aperture ofsaid transversely extending portion and partially extends into saidaperture of said cantilevered member.
 20. The apparatus for securing afirst bone portion in a fixed relationship to a second bone portion ofclaim 19, further comprising a camming member for selectively preventingrelative rotation between said spherical portion of said first clampingmember and said cantilevered member.